title: Multi-xenobiotic-resistance a possible explanation for the insensitivity of bivalves towards cyanobacterial toxins.
abstract: Filterfeeders, such as bivalves, are highly affected during toxic cyanobacterial blooms, as they are non-selective and may use the cyanobacteria as main nutrition source. The freshwater mussel Dreissena polymorpha, living in lakes and rivers coexisting with cyanobacteria, was exposed to 100 microg L(-1) microcystin-LR (MC-LR) for up to three days. MC-LR concentration in mussel tissue and surrounding media was quantified by HPLC-PDA during uptake and depuration phase, revealing an immediate, continuous uptake, and release of non-metabolized toxin, and occurrence of reincorporation. The involvement of multi-xenobiotic-resistance protein (P-glycoprotein, P-gp) on the excretion of MC-LR was evidenced by efflux and accumulation version of the Rhodamine Assay as well as on P-gp gene expression. P-gp expression was enhanced after 1 h exposure but no changes were detected after longer (72 h) exposure. P-gp enzyme activity showed a significant increase with exposure time, supporting the hypothesis that P-gp is involved in the excretion of MC-LR. Induction of biotransformation enzyme such as pi-class glutathione S-transferase (piGST) and antioxidant enzyme catalase (CAT) was immediately inhibited and returned to control values only after more than 72 h expose time. Heat shock protein 70 (hsp70) and protein phosphatase 2A (PP2A) gene expression was not changed due to the treatment with cyanobacterial toxin MC-LR.
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Dept. Inland Fisheries, Biochemical Regulation, Müggelseedamm 301, 12587 Berlin, Germany.
authors.forename: Valeska
authors.initials: V
authors.lastname: Contardo-Jara
authors.forename: Stephan
authors.initials: S
authors.lastname: Pflugmacher
authors.forename: Claudia
authors.initials: C
authors.lastname: Wiegand
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins / Q000633:toxicity*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism; D049875:Dreissena / Q000187:drug effects* / Q000378:metabolism; D018432:Drug Resistance, Multiple / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000633:toxicity; D015870:Gene Expression; D051549:Glutathione S-Transferase pi / Q000235:genetics / Q000378:metabolism; D008387:Marine Toxins; D052998:Microcystins / Q000633:toxicity*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000633:toxicity; D012235:Rhodamines; D015262:Xenobiotics / Q000633:toxicity*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001427:Bacterial Toxins; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D012235:Rhodamines; D015262:Xenobiotics; D002374:Catalase; D051549:Glutathione S-Transferase pi; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR